This invention relates to the bleaching of materials containing cotton in general and more particularly to an improved method for the continuous bleaching of cotton containing materials with peroxide.
Cold bleaching methods, in which the goods are impregnated with hydrogen peroxide and are left lying for about 24 hours are known. There are also cold bleaching methods in which the storage time is only 12 to 16 hours, but is followed by steaming for a short time in order to activate the unspent peroxide still present in the material. Hot bleaching methods, in which the goods are impregnated while hot, i.e. at 80.degree. to 100.degree. C. and are then wound on a spool contained in a thermal reaction chamber and are left there for several hours, have also been used. None of these methods are continuous. In continuous hot bleaching methods using hydrogen peroxide, bleaching times in the order of 15 to 45 minutes are presently required.
Since such times cannot be realized in a continuous process with the material being transported under tension if sufficient operating speed is to be provided, and the apparatus is not to be too large, the continuous bleaching treatment is carried out with the material deposited in folds, be it in J-boxes, on horizontal holding belts or pleated in stacks. Full white and print material can be processed while deposited in folds because in these goods there are no large uniformly dyed areas. Uniformly or substantially uniformly dyed material, however, unless it is of specially light quality, can be processed only if the material runs without folds, when in the bleaching stage, since the folds formed during the bleaching are distinctly noticeable in the subsequent dyeing. Problems are encountered in this respect particularly with expensive material which is used for outer wear, for instance, cotton material, material of polyester/cotton or also polyamide/cotton.
Heretofore, only batch processes have been customary for these goods if they were to be dyed uniformly, with the web of material wound up, i.e., stored without folds, during the dwelling time, or, through the use of so-called short time bleaching processes, in which the dwelling time is replaced by the use of appropriate chemicals. These processes are accompanied by very large consumption of chemicals. With these short time processes, operation can be continuous, of course.
It is a disadvantage of the short time processes, in turn, that the shells of the cotton cannot be removed thoroughly. Up until this time, this difficulty has been overcome only by using one of the processes with a long dwelling time.